The "twenties" grift

A couple years back, while I was still working at McDonalds (I'm a bit ashamed to admit it), a customer walked in and ordered a few things from the dollar menu. I informed him of the total, and he proceeded to pull out a hundred-dollar bill. I counted out the change, all the while they fumbled around in their pockets. I handed himthe change, upon which he "found" a couple bucks and two dimes in their pocket, asking for his Benjamin Franklin back. I looked at the fellow askance, placed the two-twenty in the drawer, and asked him for the change I had already given hiem. With some mumbled excuses, he gave it back, and I handed him his hundred in exchange - not without a few protests on his part about wanting "the rest of the money".  I could have very easily been a victim of the same grift, but my presence of mind saved the fast-food giant a few bucks - and probably saved my job in the process.